The main focus of this chemical carcinogenesis study is presently on heterocyclic amines, found in cooked meat. One of the three heterocyclic amines under study is 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). It has proven to be a highly potent hepatocarcinogen in cynomolgus monkeys, where 100% of the animals in the higher dose (20 mg/kg) group and 60% in the lower (10 mg/kg) dose group have developed malignant liver tumors so far. High cardiac DNA adducts prompted a histopathological study of hearts from necropsied tumor-bearing monkeys. All except one of the hearts studied exhibited light microscopic and/or electron microscopic evidence of myocardial damage, illustrated as widespread mitochondrial lesions and myofibrillar loss. These findings may indicate that chronic exposure to IQ in the diet may lead to toxic myocardiopathy. Thirteen monkeys which were started on Adriamycin 20 years ago were autopsied recently. Dose dependent myocardial toxicity was observed in this group. In addition, one monkey died as a result of acute leukemia and another developed a fibrosarcoma. Gender differences in tumor incidence was determined for the 33-year history of the monkey colony. The incidence of spontaneous malignant tumors was higher in males than females in cynomolgus, rhesus and African Green monkeys. Of the carcinogenically- induced tumors, the most pronounced difference between the sexes was in the group dosed with aflatoxin (72.7% of the females and 43.8% of the males developed tumors).